Powdered resorcinol-formaldehyde treated polysaccharide-reinforced elastomer masterbatches, compounds, and resulting vulcanized rubbers

ABSTRACT

Powdered elastomer masterbatches are prepared by grinding dried rubber curds which contain highly effective reinforcing agents. Such finely comminuted elastomer masterbatches provide stable powdered rubber compounds when blended with usual powdered curatives and fine particle fillers. These powdered rubber compounds are formed into finished vulcanized rubber articles by direct heat-compression molding, by extrusion from a simple machine, or by injection molding without prior high shear mixing.

United States Patent 1 Buchanan et al.

[ Jan.30,1973

[54] POWDERED RESORCINOL- FORMALDEHYDE TREATED POLYSACCHARIDE-REINFORCEDELASTOMER MASTERBATCHES, COMPOUNDS, AND RESULTING VULCANIZED RUBBERS[75] Inventors: Russell A. Buchanan; Charles R.

Russell, both of Peoria, Ill.

[73] Assignee: The United States of America as represented by theSecretary of Agriculture [22] Filed: Feb. 28, 1972 [21] Appl. No.:230,098

, Related U.S. Application Data [62 Division of Ser. No. 58,187, July24, 1970, Pat. No.

[52] U.S. Cl .1. ..260/17.2, 260/749 [51] Int. Cl ..C08c 9/12, C08f45/14 [58] FieldofSearch ..260/17.2

[56] References Cited UNlTED STATES PATENTS 3,673,136 6/1972 Buchanan..260/17.4 BB

Primary Examiner-William H. Short Assistant Examiner-Edward WoodberryAtt0rney-R. Hoffman et al.

[57] ABSTRACT 6 Claims, N0 Drawings POWDERED RESORCINOL-FORMALDEHYDETREATED POLYSACCIIARIDE-REINFORCED ELASTOMER MASTERBATCIIES, COMPOUNDS,AND RESULTING VULCANIZED'RUBBERS This is a division, of application Ser.No. 58,187 filed July 24,1970 now U.S. Pat. No. 3,673,136.

A nonexclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStatesG overnment, with the power to grant sublicenses for suchpurposes,- is hereby granted to the Government of the United States ofAmerica.

BACKGROUND OF THE INVENTION This invention relates to processes forproducing powdered elastomer compositions. The invention morespecifically relates to powdered elastomer compositions from whichvulcanized rubber can be directly prepared. A particular aspect of theinvention concerns extensions of and improvements over the inventionsdescribed by Buchanan et al., U.S. Pat. Nos. 3,442,832, 3,480,572, andcommonly assigned copending application Ser. No. 859,195, filed Sept.18, 1969, of Stephens et al., which disclosures are incorporated hereinby reference.

The instant invention provides the first example of potentially'low-cost, storage-stable, general-purpose, powdered rubber compoundssuitable for a wide range of applications. It is well known thatavailability of general-purpose elastomer compounds in powdered form hasthe possibility of revolutionizing the rubber industry by eliminatingthe need for costly high shear mixing and the consequent need for heavyduty mixing equipment typified by Banbury mixers. It is desirable tohave powdered elastomers such that powder processing techniques commonto the plastics industry can be employed in manufacture of rubber goods.

Finely divided elastomers have been prepared by spray drying of latexmixtures, but this method is inherently high in cost and has many otherattendant difficulties as discussed by Hedberg et al., U.S. Pat. No.3,194,781. Also, powdered elastomers have been prepared byco-coagulation with water glass as disclosed by Maass et al., U.S. Pat.Nos. 3,190,851 and 3,257,350; but this method is also impracticallyexpensive besides giving products of limited application because of thehigh silica loading (50 parts per 100 parts elastomer, phr). Certainother methods for preparation of powdered elastomers have been suggested or attempted; for example, making a 1 percent solution ofelastomer, then cooling the solution below the glass transitiontemperature of the elastomer before coagulation. However, all suchmethods involving very low temperatures and/or high dilutions are alsoeconomically prohibitive.

What has been needed is a low-cost, high-production-rate process forcomminuting elastomers to fine particle size. But it is well known thatdirect grinding of ordinary elastomer crumb or slab is impracticalbecause the heat generated causes it to become extremely tacky and itsticks to internal mill parts, clogging the machine as well as causingexcessive power consumption. Elastomers have been ground or pelletizedto coarse powders (ca. Vs-inch particle diameters) by admixture ofundesirable and expensive detackifying agents such as polystyrene dust.

Elastomers mightalso be ground under extreme conditions at dry icetemperatures below the polymer brittle point. However, all prior artcomminuted elastomers reagglomerate or more usually adhere to form asingle mass upon storage. So also do most of the powders formed by spraydrying or co-coagulation methods. 7

1n the United States, one powdered specialty elastomer has recentlybecome available, a nitrile at a high premium price as compared to thesame slab elastomer. The price premium on this powdered nitrile atteststo both the difficulty of production and the utility of powderedelastomers. Despite widespread interest, free-flowing, general-purpose,powdered elastomers remain unavailable because no practical method fortheir preparation existed prior to our invention. 7 i

In the patents of Buchanan et al., supra, it was disclosed thatpolysaccharide-elastomer coprecipitates are obtained by simultaneouslycrosslinking polysaccharide and destabilizing latex particles inmixtures of polysaccharide solutions and latices. Thepolysaccharide-elastomer coprecipitates are oven dried to providehard-curd particles in which the dry polysaccharide constitutes thecontinuous phase and elastomer particles the discontinuous phase. In theBuchanan patents it was disclosed that extensive high shear mixing as ona differential roll mill or equivalent machine was required to producephase inversion and give useful rubber products with a fine particledispersion of polysaccharide in elastomer matrix. In the copendingapplication Ser. No. 859,195, it was further disclosed that hotmechanical working in a closed machine with moisture present during thephase inversion is advantageous. This phase inversion is obviously acritical step in the process of producing polysaccharide-reinforcedrubbers since such composite materials must have an elastomeric matrixin order to have high elastic properties or rubbery character.Furthermore, reinforcement of elastomers requires the good dispersion ofhard, fine particle filler achieved by breaking up the originalpolysaccharide matrix during the phase inversion.

A primary object of the invention is to provide powdered rubbercompounds suitable for direct heat-compression or injection molding togive finished, vulc'anized rubber products, thus making the powderprocessing techniques long employed by the plastics manufacturingindustry available to rubber processors for the first time. Anotherobject of the invention is to provide powdered elastomer masterbatchessuitable for direct blending with curatives and other ingredients toprovide completely and thoroughly mixed compounds ready for molding andvulcanizing, thereby completely eliminating or greatlyreducing the needto employ expensive, conventional high shear rubber mixing equipment andprocesses.

Another object of the invention is to provide a method for producinggeneral-purpose elastomer powders by a low-cost, high-production-rate,direct grinding process.

In accordance with the above-stated objects, we have discovered a methodfor making powdered polysaccharide-reinforced elastomer masterbatches.The method comprises coprecipitating polysaccharides with elastomers,drying the coprecipitates, and comminuting the coprecipitates. Thepolysaccharide can be any one of the following: starch xanthide, zincstarch xanthate, resorcinol-formaldehyde-treated zinc starch xanthate,lignin and starch xanthide in combination,resorcinol-formaldehyde-treated gelatinized starch, and their cerealflour analogs. Elastomers can be styrene-butadiene rubber, oil-extendedstyrene-butadiene rubber, nitrile rubber, and phenol-formaldehyderesin-extended nitrile rubber.

Storage-stable, readily curable, powdered polysaccharide-reinforcedrubber compounds can be made by blending powdered polysaccharidereinforced elastomer masterbatches with normally used rubber curatives(i.e., those used in industry such as zinc oxide, sulfur, antioxidantpowder, etc.). Besides the curatives, fillers and extenders such asclay, highly reinforcing silica, or carbon black can be incorporated inthe rubber compounds.

We have also discovered a method for making vulcanized rubber by directshaping, molding, and curing of powdered polysaccharide-reinforcedrubber compounds with very little prior shear mixing. The shaping andmolding are accomplished by the combined action of heat and compressionon the powder.

DETAILED DESCRIPTION OF THE INVENTION We found that the critical phaseinversion in polysaccharide-rubber coprecipitates may be made to occurby a process of grinding followed by a heat compression or other moldingstep in which only very little or no flow of elastomer occurs. Rubberarticles equivalent to products obtained by practicing the inventions ofthe BUchanan patents may be made by fine grinding driedpolysaccharide-elastomer curd and then molding the resulting powder.Such articles are fully satisfactory for a large variety ofapplications. This accomplishment seems at first to be completelycontradictory and opposed to all our earlier teaching that high shearmixing and mechanical working to bring about extensive flow of elastomermatrix is necessary to produce phase inversion as needed for rubberyproperties. However, having made the unexpected discovery of the presentinvention, we now reason that grinding of the dry polysaccharide-rubbercurd produces incipient phase inversion by breaking up the continuouspolysaccharide phase to fine particle size in combination with a verylimited hot-flow which may occur during impact in conventionalcomminuting apparatus. Then the phase inversion process must becomecompleted as a result of the further very limited flow occurring in theheat-compression or other molding process. The above explanation may notbe entirely correct, but, regardless of the mechanism involved, it isnow apparent that phase inversion from rubber particles in apolysaccharide matrix to polysaccharide particles in a rubber matrix mayconveniently be accomplished by a process involving comminuting drypolysaccharide-rubber coprecipitates followed by heatcompression,extrusion, or injection molding.

We have found that grinding of dry polysaccharideelastomer coprecipitateis facile and gives free-flowing, fine powders. The resulting powderedmasterbatches are easily blended with usual powdered curatives to givestorage-stable powdered rubber compounds.

These powdered compounds can be directly molded into rubber articles inordinary heated compression molds. The powders can also be formed intofinished rubber articles by extrusion from a simple machine with noprior shear mixing; hence, also by injection molding. When desirable,the powdered polysaccharide-rubber compounds per se can beadvantageously shaped into mold blanks or further mixed with additionalingredients on differential rolls, or with extruders before shaping intomold blanks. Thus', much less shear mixing is required than forconventional rubber processing.

For grinding polysaccharide-rubber compositions, any of the commoncommercial comminuting machines may be employed, i.e., impact mills suchas hammer, Wiley, and pin mills, etc. Grinding may include air or screenclassification with recycle of coarse fractions to the grinders asconventionally practiced in order to further reduce average particlesize. We find it advantageous, but not essential, to incorporate smallamounts of anticaking substances into powdered rubber masterbatches.Fine particle fumed or hydrated silicas are preferred because thesematerials are further useful for their reinforcing ability in thefinished rubbers. Generally, we employ up to 10 phr of hydrated silica(PPG l-li-Sil 215) which has been pelletized and is thereforeadvantageously added during the grinding operation to achieve bothdisintegration of pellet and distribution throughout the powdered rubbermasterbatch. Additional fillers and extenders .such as clay, highlyreinforcing silica, and carbon black can also be used.

Compounding of polysaccharide-rubber masterbatch powders may beaccomplished with V or ribbon blenders if added ingredients are finepowders. lf flaked, pelletized, or encapsulated compounding ingredientsare added, high-speed rotary blade powder mixers, such as the WaringBlendor or l-lenschel mixer, are preferred.

This invention may be practiced with any of the polysaccharide-rubbercompositions disclosed in the reference US. Patent Nos. (3,442,832 and3,480,572) and copending application Ser. No. 859,195. Accordingly, anyelastomer available in latex form may be employed including naturalrubber or preferably synthetic elastomers such as nitrile and SBR.Suitable polysaccharides include starches, starch derivatives,

cereal flour, and derivatives thereof. Examples of ap-' plicable starchproducts are gelatinized starches, aminated starches, xanthatedstarches, resin-treated starches, starch xanthides, and similarderivatives as well as their cereal flour analogs, etc. Polysaccharideloading must exceed about 15 phr for easy grinding. There is no upperlimit on polysaccharide loading, but the cured products undergo atransition from elastic vulcanized rubbers to rigid thermoset plasticsas starch loading increases above about phr. For elastic vulcanizedrubbers, we prefer to use relatively low polysaccharide loadings, froml5 ,to 30 phr, in order to allow more freedom for addition ofconventional fillers during compounding, thus increasing the area forapplication of the powdered elastomer masterbatches. For rigid thermosetplastic applications, we prefer to use relatively high polysaccharideloadings, from 100 to 400 phr, so that the total composition containsnot more than about 70 weight percent eiastomer plus resin combined.

The following examples are included as further illustrations of theinvention but not as limitations thereon.

EXAMPLE 1 The starting materials included type l502-SBR(styrene-butadiene) latex containing 20.5 percent total solids and apercent aqueous starchxanthate solution with xanthate degree ofsubstitution (D.S.) of 0.1 1.

For a starch xanthide-SBR-l502 coprecipitate containing phr starch (20parts starch per 100 parts SBR), a homogeneous mixture was preparedcontaining 800 g. starch xanthate solution, 1,950 g. SBR-l502 latex, 8g. of 50 percent styrenated phenol antioxidant emulsion, and 6 g. sodiumnitrite. This mixture was stirred for 30 minutes, then 175 ml. of 2 Nsulfuric acid were slowly added dropwise with stirring to give a pH of4.0-4.5 and maintain it for 10 minutes. This treatment coprecipitatedstarch xanthide and SBR-l502 elastomer as large curd particles. Thecurds were recovered by filtration, washed once by suspension in water,then dried in a forced draft oven at 70 C. to give 476 g. of driedstarch-rubber coprecipitate.

Another starch xanthide-SBR-l502 coprecipitate having 30 phr starch wasprepared in the same manner One portion of each compound wasconsolidated into mold blanks suitable for preparing standard ASTM testspecimens by passing through a tight nip on a differential roll mill forthree passes, then sheeting out to the required thickness with a minimumof further milling. This mold blank forming process required less thanone-tenth of the high shear mixing time needed for conventional rubberprocessing, i.e., as described by ASTM method Dl568a for example.Oscillating disc rheonleter cure data were obtained using thesemillformed blanks for each compound, and all vulcanized test specimenswere prepared using the rheometer optimum cure time at 150 C.

The other portion of each powdered rubber com pound was subdivided, andtest specimens were prepared by direct powder molding. A thin flatrubber sheet for tensile specimens was prepared by molding powderdirectly between flat plats. A small rubber dish was compression moldedand cured for examination. Rods, A inch in diameter, were prepared frompowder feed by extrusion at 125 C. with a Brabender- Plasticord'erequipped with 10/1 length to diameter ratio extrusion head and thenpost-curing the extrudate in an oven.

Representative physical test data for these various specimen types aregiven in the following table:

Ultimate Cure Tensile elonga- Dish,utility, time, Hardness, strength,tion, and appear- Stareh loading, phr. Treatment rnin. Shore A p.s.i.percent ance Mill consolidation 17 70 1, 500 i 475 20 Powder molding 17760 220 Excellent.

Powder extrusion 17 1.155 {Mill consolidation 17. 5 77 1, 110 330Powdermolding. 17.5 1,050 200 Do. Mill consolidation"; 15. 5 83 l, 620260 45 Powder molding 15. 5 1, 070 130 Good Powder extrusion 15. 5 1,090

with the same quantities of latex and antioxidant, but using 1,200 g.starch xanthate solution, 7.6 g. sodium nitrite, and 253 ml. of 2 Nsulfuric acid. This gave 503 g. of dried starch-rubber coprecipitate.

A third starch xanthide-SRB-l502 coprecipitate having 45 phr starch wasalso prepared based on the same amount of latex. This product weighed580 g.

Since the oven-dried curds were too large for the feed screw of ourlaboratory hammermill, each product was first ground to pass a 3-meshscreen on a small Wiley mill. The coarse ground coprecipitates were thenground through a l6-mesh screen by an ordinary agricultural-typehammermill. Each powder was then mixed with 20 g. of hydrated silica ina Waring Blendor for 30 seconds. Screen analyses of the resultingfreeflowing powders gave the following values:

Masterbatch Particle diameters, smaller than composition 1,410 [law ,i590 n 420 [L 350 a 20 phr starch 100 98.4 90.7 67.6 50.8 30 phr starch100 96.5 78.3 50.l 38.3 45 phr starch I00 98.6 93.4 80.4 70.4

Each masterbatch powder was mixed with l phr flake stearic acid, 4 phrzinc oxide, 2 phr sulfur, 2 phr antioxidant powder, l.5 phr benzothiazyldisulfide accelerator, and 0.1 phr tetramethylthiuram disulfidesecondary accelerator for 30 seconds at high speed in a Waring Blendor.Each resulting rubber compound was then divided into two equal portions.

Remaining portions of these powdered starch xanthide-SBR-l502 compoundswere stored at room temperature for 10 weeks. At the end of this storageperiod, they remained free-flowing, and their rheometer cure curvesremained unchanged, i.e., completely identical with the initial curvesmade soon after compounding. Thus, these powders were completely stableto indefinitely long storage.

Although the above physical test data appear to indicate that millconsolidation of the powdered compounds results in better vulcanizatestrength than the other treatments, the difference in test values is duein part to inaccuracies associated with testing the nonstandardspecimens prepared by the powder-forming processes. The inaccuraciesarise because such specimens are hard to clamp properly in our testmachine. We believe that the properties of the extruded shapes areactually fully equivalent to those of the mill consolidated specimens.The data clearly show that rubber articles with technically useful andacceptable properties can be prepared by direct molding of thisinventions powdered compounds and that these compounds are suitable fordirect feeding to screw injection molding machines.

EXAMPLE 2 Latex andstarch xanthate starting materials were the same asin Example 1.

For a zinc starch xanthate-SBR-l502 coprecipitate a The above dataclearly show containing 20 phr starch, a homogeneous mixture wasprepared containing 800 g. starch xanthate solution, 1,950 g. SBR-1502latex, and 8 g. of 50 percent styrenated phenol antioxidant emulsion.This mixture was agitated for 30 minutes; then 24 ml. of 2 N sulfuricacid were added dropwise, followed by rapid addition of 198 ml. of Mzinc sulfate solution. The resulting coprecipitate was recovered byfiltration and dried, without washing, in a forced draft oven at 70 C.,giving 487 g. of product.

Other zinc starch xanthate-SBR-l 502 products containing 30 phr and 45phr starch, respectively, were preparedby the same process usingincreased amounts of starch xanthate solution and acid but the samequantities of other reagents. There were 536 g. and 611 g. of these twoproducts, respectively.

All three samples were ground by the procedure of Example 1 except thatthe 20 g. of hydrated silica were added before grinding through thehammermill. Their screen analyses were as follows:

ditional high-reinforcing agents. Thus, his a very versatile productwith a wide range of applications.

EXAMPLE 3 Four powdered masterbatches were prepared from startingxanthate solutions containing 10 percent of corn flour, soft wheatflour, hard wheat flour, or unmodified corn starch, respectively. Thesemasterstarch products, respectively. Screen analyses were as follows:

Masterbatch Particle diameters, smaller than com sition 1,410 p. 840 u590 p. 420 a 350 u 20 p r starch 100 87.5 74.3 55.7 45.7 30 phr starch100 96.2 86.2 65.2 50.7 '45 phr starch 100 99.5 94.4 77.1 64.9 e

- Masterbatch Particle diamgters, smalgler than 20 so composition 1,410p. 40 p. 0 a a 3 t These masterbatch powders were compounded with Comflour '00 97.8 856 599 46.6 a Waring Blendor as in Example 1 except thataddition Soft wheat of zinc oxide was not required. Vulcanized test 2:3when 63 509 specimens were prepared as in Example 1 and their test 100971 863 66'] 53.9 values are given below: Starch 100 95.0 79.6 59.1 51.2

Ultimate Cure Tensile elonga- Dish,utility, time, Hardness, strength,tlon, and appear Starch loading, phr. Treatment min. ShoreA p.s.i.percent once Mill consolidation 21 63 1, 860 720 Powder molding 21 1,150570 Excellent 20 translucent.

Powder extrusion 1,163 Mill consolidation 1, 600 510 30 "{Powder molding1,110 380 Do.

Powder extrusion 1, 800 Mill consolidation 1, 320 450 45 {Powdermo1ding. 710 Satisfactory.

Powder extrusion 840 that zinc starch xanthate-SBR powdered rubbercompounds are fully equal or superior to the starch xanthide containingpowders. We believe that the compound containing Abrasion Cure TensileUltimate,

time, Hardness, resistance, strength, elongation Product Treatment min.Shore A percent p.s.i. p.s.i.

Mill consolidation 30 74 109 2, 180 480 Corn ilour Powder molding 30 1,460 320 Powder extrusion 30 Mill consolidation 30 76 133 2, 040 416 Sortwheat ilour Powder molding 30 1, 600 310 Powder extrusion 30 2, 085

Mill consolidutlon.. 27 77 1,830 360 11 ard wheat flour Powdermolding... 1, 680 350 Powder extrusion 2, 025

Mill consolidation 2, 200 400 Starch Powder molding... 1, 510 270 Powderextrusion 30 1, 800 1 only 20 phr zinc starch xanthate is especiallyuseful because of the strong, very elastic, light-colored, translucentrubber articles which can be directly molded from this powder. Becauseit has a low starch loading, this powdered compound is very amenable toextension with additional fillers and extenders as well as with ad- Theabove surprisingly good abrasion resistance values were obtained withthe DuPont abrader and are relative values. Vulcanizates made formcommercial type 1606, 52 phr l-lAF black reinforced, SBR masterbatchwere assigned abrasion resistance value of percent.

Each of the above powdered compounds gave an excellent highly elastic,brown, translucent dish with a polished surface by direct molding frompowder.

This example illustrates that a variety of low-cost amylaceous materialscan be employed in place of EXAMPLE 5 A hot corn flour paste containing19.96 percent solids was prepared by steam-jet cooking at 340 F. with aPenick and Ford laboratory cooker described in their U.S. Pat. No.3,133,836. Similarly, a hot unmodified corn starch paste was preparedcontaining 19.71 percent solids.

Homogeneous mixtures were made immediately from 545 g. of the hot cornflour paste and 572 g. of the hot starch paste, respectively, with added8 g. of 50 percent sodium hydroxide, 1,950 g. of SBR-l 502 latex, 8 g.of 50 percent styrenated phenol antioxidant emulsion, 4.9 g. ofresorcinol, and 4.0 g. of paraformaldehyde. Each of these mixtures wasstirred 30 minutes then coprecipitated by addition of 185 ml. M zincsulfate solution. The soft curd products were recovered by filtrationand dried in a forced draft oven at 70 C. Dry weights were 527 g. and519 g. for corn flour resin and starch resin products, respectively.They contained 30 phr of resin-treated amylaceous material wherein 0.06mole of resorcinol per 162 g. of cereal raw material was incorporated.

These products were ground by the procedure of Example 2 with results asfollows:

Particle diameters, smaller than Product They were compounded by mixingwith powdered curatives in the Waring Blendor, optimum curing conditionswere determined, and vulcanized test specimens 4 3, each powderedcompound gave vulcanizates with surprisingly good abrasion resistance.They also gave excellent quality dishes by direct molding from powder.

EXAMPLE 5 Four lignin-containing starch xanthide-SBR-ISOZ coprecipitateswere prepared as described in Example 1 in amounts based on 1,950 g. ofthe starting latex.

10 The quantities of other reagents were varied to give either or phrstarch loading, and purified commercial lignin was added in amountsgiving either 13 or 26 phr loading. Identification and composition ofthese samples follow:

Sample No. 12 was ground by the procedure of Example 1. No hydratedsilica was subsequently addedeven though lignin is somewhat deleteriousin its effect on caking of these powders. Sample No. 78 had 5 phrhydrated silica incorporated during grinding as in Example 2. SamplesNo. 80 and 81 were ground once through the hammermill with added 3 phrhydrated silica then screened on a 30-mesh screen. Then the coarsefraction from samples 80 and 81 was reground through the hammermill withan additional added 2 phr hydrated silica and recombined with its finefraction. Screen analysis of these powdered masterbatches follow:

Particle diameters, smaller than Sample No. 1,410 p. 840 p. 590 p. 420p. 350 p. 78 100 94.7 82.0 56.2 40.7 80 100 98 94.5 80.6 62.3 40 12 10063.3 35 8.4 81 100 98.9 95.4 77.6 58.9

Vulcanizates made by compounding and curing the above powderedmasterbatches had the following prowere prepared. perties;

Cure Abrasion Tensile Ultimate, time, Hardness, resistance, strength,elongation Product Treatment min. Shore A percent p.s.i. p.s.i.

Mill consolidation 30. 100 1, 380 710 Corn flour Powder molding 30. 51,140 430 Powder extrusion 30. 5 1,010 Mill consolidation 36 1.10 1, 530500 Starch Powder molding 35 1, 420 370 Powder extrusion 35 167 CureTear Tensile Ultimate time, Hardness, strength, strength, elongationSample No. Treatment min. Shore A lb./in. p.s.i. percent Millconsolidated 46 67 253 2, 340 815 78 Powder molded 46 1, 720 790 Powderextrusion 46 1, 595

Mill consolidated 23 209 2, 600 660 80 Powder molded... 23 1, 980 600Powder extrusion 23 1, 505

Mill consolidated 25 315 1, 880 365 12 Powder molded... 25 1, 040 200Powder extrusion- 25 1,

Mill consolidated 26 80 293 2, 400 500 81 Powder molded 26 980 290Powder extrusion 26 1,930

This example illustrates use of resin crosslinked gelatinized starch asan alternative to starch xanthate derivatives in practice of theinvention. Resulting vul-' canizates have somewhat different propertiesthan are obtained with xanthate derivatives. But as in Example Thisexample illustrates that the invention can be practiced advantageouslywith the previously disclosed synergistic starch-lignin reinforcingagents. Each of the above powdered rubber compounds gave high-qualityrubber articles by direct molding.

dispersible phenol-formaldehyde resole syrup contain- 5 Samples 87 and88 were powder blended with rubber curatives, cured, and tested as inprevious examples. Their vulcanizate properties are tabulated below:

Ultimate Cure Tensile elonga- Dish, time, Hardness, strength, tion,utility, and Sample No. Treatment min. Shore A p.s.i. percent appearanceMill consolidated 24. 5 78 1, 640 360 87 Powder molded 24. 5 1, 400 250Excellent Powder extrusion 24. 5 1,190 Mill consolidated 34. 9O 2, 080340 88 Powder molded 34. 0 1, 160 130 Do.

Powder extrusion 34. 0 1,210

mg 66.8 percent solids, and Chemigum 236 NBR (nitrile)acrylonitrile-butadiene latex containing 39.9 percent solids.

Sample No. 87 contained 20 phr of resorcinol-formaldehyde-treated zinccorn flour xanthate and no phenol-formaldehyde resin. A homogeneousmixture was prepared from 800 g. of xanthate solution, 1,002 g. of NBRlatex, 8 g. of 50 percent antioxidant emulsion, 2.2 g. of resorcinol,and 4.8 g. of 37 percent formalin.

Samples 90 and 91 were treated as phenolic resin molding compounds.Sample 90 was blended in a Waring Blendor with 2.0 g. stearic acid, 27.7g. calcium 0xide, 4.0 g. sulfur, 3.0 g. antioxidant, 3.0 g. benzothiazyldisulfide, and 0.2 g. tetramethylthiuram disulfide. Sample 91 wasblended with 0.7 g. stearic acid, 26.4 g. calcium oxide, 1.4 g. sulfur,1.0 g. antioxidant, 1.0 g. benzothiazyl disulfide, and 0.1 g.tetramethylthiuram disulfide. Both these powder compounds were den- The8 for 30 u i of sified by passing through the nip of a steam-heated dif-2 N Su ur: 86 were added dropwlse f0|l0Wed y ferential roll mill forfive passes. The densitied material rapid addit on f 3 1111- Of M ZincSulfate Solution was removed from he roll with a doctor knife after eachThe coprecipitated curd was recovered by filtration pass Th d ifi d d rswere then cured 20 and dried in a forced draft Oven at giving 507 8-minutes at 150 C. in various compression molds. of Product Moldedarticles were produced including dishes of the Sample 88 cQmamed 25 P ofresorcmol'fol" type examined in previous examples. These articlesmaldehyde'treated Zmc conlflour Xanthate P P were thermoset plasticswith hard smooth finish, excel of phenol'fol'maldehyde m- It was P p ithe lent appearance, good water resistance, and high-im- Same mannef asabove 1 the safne quantities of pact resistance. Articles made fromsample 90 were latex, antioxidant, and 21116 but using 1,000 g. ofSlightly fl ibl xanthate, 148 g. of resole syrup, 2.7 g. of resorcinol,6.1 g. of formalin, and 50 ml. of 2 N acid. The dry product EXAMPLE 7weighed 626 g. A free flowin g powdered Zll'iC starch xanthate-oil-ex-Sample 90 coijtamed 100 phr of resorcmol'for' tended elastomermasterbatch was prepared by the maldehyde'treated Zmc com flour xanihateand 100 40 method of Example 2. It contained 20 parts starch and phrphenol-formaldehyde resmi It was 10 parts silica per 100 parts oil pluselastomer; the oil coprgclpltageld method 2 to elastomer ratio was 1/2.The masterbatch contained Xam 5 i 296 2 8 syrup 350 g. of Sunthene 3120napthenic extender oil and resorclnol, 13 g. formalin, 4 g. antioxidantemulsion, 700 g of SBR type 1713 elastomer in a total sample 115 m1. of2N sulfuric acid, and 198 ml.M zinc sulfate. weight of 1 366 g Screenanalysis of the powder drylproNducgt 2 h f l f masterbatch showed thatmore than 54 percent of its amp e me p r o resorcmo or particles weresmaller than 350 t with none larger than maledhye-treated zmc corn flourxanthate and 400 phr l 410 p phenol-formaldehyde resin. it was made asabove using e powdered masterbatch was divided mto f1ve 223 gzgi f g h gz g fi ggf ib ig g 260-g. portions and a sixth remaining portion of 66g. g .?p z formalin 265 ml gs'ulfuric acid Each portion was compoundedwith rubber curatives as in previous examples but with additionalfillers except g :31 T dry g f samples 92-1 and 92-6 which had 110additional fillers. ac pm 95 as 6 Sample 92-2 had an additional 30 phrof hydrated sil- Three phr of hydrated silica were added to sample No.55 ica 924 had 52 p hard y had 18 phr ASTM 87 during compounding but notto the others. All gave refrence black No. 2 (HAP): had 36 phr of theperfectly frevef'flowmg powders as follows No. 2 reference black, and92-6 was the 66-g. portion of masterbatch compounded exactly as 92-1 forcoml' Smancmla" 6O parative powder molding. The first five of thesecomgz 1 M0 840 590 420 3 pounds were mill consolidated into mold blanks,cured, 5 3 5 and test specimens prepared. Vulcanizate properties 88 10098.6 93.1 egg W e follow.

Tear 300% Tensile Ultimate Spec fic Hardness, strength, modulus,strength, elongation, Sample No gravrty ShoreA 1b./in. p.s.i. p.s.i.percent 1. 085 49 149 480 1, 080 700 1.185 as 221 e 1, 730 150 1. 289 63204 650 1, 580 780 1. 141 60 201 920 1, 800 560 1. 186 70 230 1, 360 2,480 02-6 e00 250 It is evident from he foregoing data that thisinvention provides even highly oil-extended, general-purpose elastomerpowders entirely suitable for compounding with high loadings of avariety of additional reinforcing agents, fillers, and extenders.

We claim:

1. Powdered resorcinol-formaldehyde-treated zinc cereal xanthate-SBRelastomer masterbatches containing about 30 phr of a material selectedfrom the group consisting of refined starch and cereal flours, havingnearly all particles below 1,410 a diameter and more than 46 weightpercent below 350 p. diameter, and which provide vulcanized rubbershaving greater than about 1,450 p.s.i. tensile strength, greater thanabout 74 Shore A hardness, and greater than about 270 percent ultimateelongation.

2. Powdered resorcinol-formaldehyde-treated gelatinized cerealproduct-8BR elastomer masterbatches containing about '30 phr of amaterial selected from the group consisting of refined starch and cerealflour, having nearly all particles below 1,410 diameter and more than 58weight percent below 590 p. diameter, and which provide vulcanizedrubbers having greater than about 1,010 p.s.i. tensile strength, greaterthan about 59 Shore A hardness, and greater than about370 percentultimate elongation.

3. Powdered resorcinol-formaldehyde-treated zinc corn flour xanthate-NBRelastomer masterbatches containing from 20 to 400 phr corn flour andfrom to 400 which provide vulcanized rubbers having greater than about1,160 p.s.i. tensile strength, greater than about 78 Shore A hardness,and greater than about percent ultimate elongation.

4. Reinforced vulcanized rubber prepared from powderedresorcinol-formaldehyde-treated zinc cereal xanthate-SBR elastomermasterbatches described in claim 1 blended with normally used rubbercuratives, and that has. greater than about 1,450 p.s.i. tensilestrength, greater than about 74 Shore A hardness, and greater than about270 percent ultimate elongation.

5. Reinforced vulcanized rubber prepared from powderedresorcinol-formaldehyde-treated gelatinized cereal product-8BR elastomermasterbatches described in claim 2 blended with normally used rubbercuratives, and that has greater than about 1,010 p.s.i. tensilestrength, greater than about 59 Shore A hardness, and greater than about370 percent ultimate elongation.

6. Reinforced vulcanized rubber prepared from powderedresorcinol-formaldehyde-treated zinc corn flour xanthate-NBR elastomermasterbatches described in claim 3 blended with normally used rubbercuratives, and that has greater than about 1,160 p.s.i. tensilestrength, greater than about 78 Shore A hardness, and greater than about130 percent ultimate elongation.

1. Powdered resorcinol-formaldehyde-treated zinc cereal xanthate-SBRelastomer masterbatches containing about 30 phr of a material selectedfrom the group consisting of refined starch and cereal flours, havingnearly all particles below 1,410 Mu diameter and more than 46 weightpercent below 350 Mu diameter, and which provide vulcanized rubbershaving greater than about 1, 450 p.s.i. tensile strength, greater thanabout 74 Shore A hardness, and greater than about 270 percent ultimateelongation.
 2. Powdered resorcinol-formaldehyde-treated gelatinizedcereal product-SBR elastomer masterbatches containing about 30 phr of amaterial selected from the group consisting of refined starch and cerealflour, having nearly all particles below 1,410 Mu diameter and more than58 weight percent below 590 Mu diameter, and which provide vulcanizedrubbers having greater than about 1, 010 p.s.i. tensile strength,greater than about 59 Shore A hardness, and greater than about 370percent ultimate elongation.
 3. Powdered resorcinol-formaldehyde-treatedzinc corn flour xanthate-NBR elastomer masterbatches containing from 20to 400 phr corn flour and from 0 to 400 phr of phenol-formaldehydeextender resin, having nearly all particles below 1,410 Mu diameter andmore than 69 weight percent below 350 Mu diameter, and which providevulcanized rubbers having greater than about 1, 160 p.s.i. tensilestrength, greater than about 78 Shore A hardness, and greater than about130 percent ultimate elongation.
 4. Reinforced vulcanized rubberprepared from powdered resorcinol-formaldehyde-treated zinc cerealxanthate-SBR elastomer masterbatches described in claim 1 blended withnormally used rubber curatives, and that has greater than about 1,450p.s.i. tensile strength, greater than about 74 Shore A hardness, andgreater than about 270 percent ultimate elongation.
 5. Reinforcedvulcanized rubber prepared from powdered resorcinol-formaldehyde-treatedgelatinized cereal product-SBR elastomer masterbatches described inclaim 2 blended with normally used rubber curatives, and that hasgreater than about 1,010 p.s.i. tensile strength, greater than about 59Shore A hardness, and greater than about 370 percent ultimateelongation.